Photoresist cross-linker and photoresist composition comprising the same

ABSTRACT

The present invention is directed to photoresist cross-linkers selected from the group consisting of a cross-linker monomer represented by following Chemical Formula 1, and homopolymers and copolymers thereof. Such cross-linkers are suitable for use in photolithography processes employing KrF (248 nm), ArF (193 nm), E-beam, ion-beam or EUV light sources. 
     &lt;Chemical Formula 1&gt;

FIELD OF THE INVENTION

The present invention relates to cross-linking agents (“cross-linkers”)usable for negative photoresist compositions and photoresistcompositions comprising the same. More specifically, it relates tocross-linking agents used in photoresists suitable for photolithographyprocesses using a KrF (248 nm), ArF (193 nm), E-beam, ion beam or EUVlight source when preparing a microcircuit of a highly integratedsemiconductor element, and photoresist compositions employing the same.

BACKGROUND OF THE INVENTION

Recently, chemical amplification type DUV (deep ultra violet)photoresists have proven to be useful to achieve high sensitivity inprocesses for preparing microcircuits in the manufacture ofsemiconductors. These photoresists are prepared by blending a photoacidgenerator with polymer matrix macromolecules having acid labilestructures.

According to the reaction mechanism of such a negative photoresist, thephotoacid generator generates acid when it is irradiated by the lightsource, and the main chain or branched chain of the polymer matrixmacromolecule is cross-linked with the generated acid to form across-linked structure. Thus, the portion exposed to light cannot bedissolved by developing solution and remains unchanged, therebyproducing a negative image of a mask on the substrate. In thelithography process, resolution depends upon the wavelength of the lightsource - the shorter the wavelength, the smaller the pattern that can beformed. However, when the wavelength of the light source is decreased inorder to form a micro pattern [for example, in the case of using 193 nmwavelength or EUV (extremely ultraviolet) light], it is disadvantageousin that the lens of the exposing device is deformed by the light source,thereby shortening its life.

Melamine, a conventional cross-linker, has a limited number (three) offunctional groups which can form a cross-linkage with acid. Further, alarge amount of acid must be generated when melamine is used as across-linker, because acid is consumed by the cross-linking reaction. Asa result, high-energy light exposure is required for such cross-linkingagents.

In order to overcome the disadvantages described above, chemicalamplification type compounds that cross-link with a photoresist polymer(also referred to herein as a “photoresist resin”) and use less amountsof energy are desirable. However, such chemical amplification typecross-linkers have not yet been developed.

SUMMARY OF THE INVENTION

The object of the present invention is to provide novel photoresistcross-linkers, and a process for the preparation thereof.

Another object of the present invention is to provide photoresistcompositions comprising the cross-linkers, and a process for thepreparation thereof.

Still another object of the present invention is to provide asemiconductor element manufactured from the photoresist composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 10 show photoresist patterns prepared by usingcross-linkers obtained from Examples 11 to 20.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In one aspect, the present invention provides a cross-linker monomerrepresented by the following Chemical Formula 1:

<Chemical Formula 1>

wherein X₁ and X₂ individually represent CH₂, CH₂CH₂, O or S; p is aninteger from 0 to 5; R₁ and R₂ independently represent straight orbranched C₁₋₁₀ alkyl, straight or branched C₁₋₁₀ ester, straight orbranched C₁₋₁₀ ketone, straight or branched C₁₋₁₀ carboxylic acid,straight or branched C₁₋₁₀ acetal, straight or branched C₁₋₁₀ alkylincluding at least one hydroxyl group, straight or branched C₁₋₁₀ esterincluding at least one hydroxyl group, straight or branched C₁₋₁₀ ketoneincluding at least one hydroxyl group, straight or branched C₁₋₁₀carboxylic acid including at least one hydroxyl group, and straight orbranched C₁₋₁₀ acetal including at least one hydroxyl group; and R₃ andR₄ independently represent hydrogen or methyl.

The cross-linkers of the present invention may comprise a cross-linkermonomer represented by the above Chemical Formula 1; a homopolymerthereof; or a copolymer thereof.

Preferably, the cross-linker is a copolymer of (i) the compoundrepresented by Chemical Formula 1 as a first comonomer and (ii) maleicanhydride as a second comonomer. Particularly preferred cross-linkersfurther comprise (iii) (meth)acrylic acid as a third comonomer and theresulting copolymer is represented by the following Chemical Formula 6.

<Chemical Formula 6>

wherein, X₁ and X₂ individually represent CH₂, CH₂CH₂, O or S; p is aninteger from 0 to 5; R₁ and R₂ independently represent straight orbranched C₁₋₁₀ alkyl, straight or branched C₁₋₁₀ ester, straight orbranched C₁₋₁₀ ketone, straight or branched C₁₋₁₀ carboxylic acid,straight or branched C₁₋₁₀ acetal, straight or branched C₁₋₁₀ alkylincluding at least one hydroxyl group, straight or branched C₁₋₁₀, esterincluding at least one hydroxyl group, straight or branched C₁₋₁₀ ketoneincluding at least one hydroxyl group, straight or branched C₁₋₁₀carboxylic acid including at least one hydroxyl group, and straight orbranched C₁₋₁₀ acetal including at least one hydroxyl group; and R₃, R₄and R₅ independently represent hydrogen or methyl; and a, b and cindividually represent the relative amounts of each comonomer.

Alternatively, preferred cross-linkers may comprise (iii) the compoundof Chemical Formula 27 as a third comonomer and the resulting copolymeris represented by the following Chemical Formula 7.

<Chemical Formula 27>

<Chemical Formula 7>

wherein, X₁ and X₂ individually represent CH₂, CH₂CH₂, O or S; Z₁ and Z₂individually represent CH₂, CH₂CH₂, O or S; p and q individuallyrepresent an integer from 0 to 5; R₁, R₂, R₈, R₉, R₁₀ and R₁₁independently represent straight or branched C₁₋₁₀ alkyl, straight orbranched C₁₋₁₀ ester, straight or branched C₁₋₁₀ ketone, straight orbranched C₁₋₁₀ carboxylic acid, straight or branched C₁₋₁₀ acetal,straight or branched C₁₋₁₀ alkyl including at least one hydroxyl group,straight or branched C₁₋₁₀ ester including at least one hydroxyl group,straight or branched C₁₋₁₀ ketone including at least one hydroxyl group,straight or branched C₁₋₁₀ carboxylic acid including at least onehydroxyl group, and straight or branched C₁₋₁₀ acetal including at leastone hydroxyl group; and R₃, R₄, R₆ and R₇ independently representhydrogen or methyl; and a, b and c individually represent the relativeamounts ratio of each comonomer.

In Chemical Formulas 6 and 7, it is preferable that the ratio a : b:c=10-89 mol %: 10-89 mol %: 1-40 mol %.

The present invention also provides a photoresist composition containing(i) a photoresist resin, (ii) a photoresist cross-linker as describedabove, (iii) a photoacid generator and (iv) an organic solvent.

The reaction mechanism of the cross-linkers according to the presentinvention is described below with reference to Reaction Scheme 1,wherein the polymer of Chemical Formula 6 is used as a cross-linker.

First, a cross-linker of the present invention is mixed with aphotoresist polymer having hydroxyl groups, and the mixture is coated ona conventional semiconductor substrate (stage 1). Then, when apredetermined region of the substrate is exposed to light, the exposedportion generates acid (stage 2). Due to the acid generated from theexposed portion, the cross-linker of the present invention and thephotoresist polymer combine together, and such cross-linking furthergenerates acid, thereby carrying out continuous chain cross-linking(stage 3).

<Reaction Scheme 1>

wherein, X₁, X₂, R₁, R₂, R₃, R₄ and R₅ are as defined in ChemicalFormula 6.

PREPARATION OF CROSS-LINKER MONOMER

The inventors have discovered that compounds represented by thefollowing Chemical Formula 1 are good negative-type photoresistcross-linker monomers.

<Chemical Formula 1>

wherein X₁ and X₂ individually represent CH₂, CH₂CH₂, O or S; p is aninteger from 0 to 5; R₁ and R₂ independently represent straight orbranched C₁₋₁₀ alkyl, straight or branched C₁₋₁₀ ester, straight orbranched C₁₋₁₀ ketone, straight or branched C₁₀ carboxylic acid,straight or branched C₁₋₁₀ acetal, straight or branched C₁₋₁₀ alkylincluding at least one hydroxyl group, straight or branched C₁₋₁₀ esterincluding at least one hydroxyl group, straight or branched C₁₋₁₀ ketoneincluding at least one hydroxyl group, straight or branched C₁₋₁₀carboxylic acid including at least one hydroxyl group, and straight orbranched C₁₋₁₀ acetal including at least one hydroxyl group; and R₃ andR₄ independently represent hydrogen or methyl.

Compounds of Chemical Formula 1 react with a photoresist polymer havinghydroxyl groups (—OH) in the presence of an acid to form a cross-linkwith the photoresist polymer. In addition, compounds of Chemical Formula1 generate another acid as a result of the cross-linking reaction toinduce a subsequent cross-linking reaction. Thus, the photoresistpolymer in the exposed region can be densely hardened to obtain highresolution of the negative pattern.

The following examples demonstrate a desirable synthesizing method forphotoresist cross-linker monomer according to the present invention:

EXAMPLE 1

Cyclopentadiene (70 g) and tetrahydrofuran (100 g) were put into a 1000ml round bottom flask and stirred. Then, a solution, which comprised 95g of acrolein (represented by following Chemical Formula 2) dissolved in100 g of tetrahydrofuran, was dropped into the solution and cooled.

<Chemical Formula 2>

After stirring for 24 hours, solvent and non-reactant were removed fromthe solution using a vacuum rotary distillator. Then, suctiondistillation was performed to obtain a monomer represented by followingChemical Formula 3.

<Chemical Formula 3>

After adding trifluorosulfonic acid (1 ml) into a round bottom flask inwhich there were 30 g of the monomer represented by the above ChemicalFormula 3 and 20 g of methanol, the resultant solution was stirred for 5hours. Potassium hydroxide was added to adjust the pH of the resultantsolution to pH 8 and then, methanol was removed therefrom using a rotaryevaporator. Finally, vacuum distillation was preformed at 50° C. toobtain a monomer represented by the following Chemical Formula 4.

<Chemical Formula 4>

EXAMPLE 2

The procedure of Example 1 was repeated, but using ethanol instead ofmethanol, to obtain a monomer of the following Chemical Formula 5.

<Chemical Formula 5>

PREPARATION OF PHOTORESIST CROSS-LINKER COPOLYMER

A photoresist cross-linker monomer according to the present inventioncan be used as a photoresist cross-linker by itself, or it can be usedto form a polymer that can also be used as a photoresist cross-linker.

Chemical Formulas 6 and 7 below represent desirable photoresistcross-linker polymers according to the present invention:

<Chemical Formula 6>

<Chemical Formula 7>

In Formulas 6 and 7, X₁, X₂, Z₁ and Z₂ individually represent CH₂,CH₂CH₂, O or S; p and q individually represent an integer from 0 to 5;R₁, R₂, R₈, R₉, R₁₀ and R₁₁ independently represent straight or branchedC₁₋₁₀ alkyl, straight or branched C₁₋₁₀ ester, straight or branchedC₁₋₁₀ ketone, straight or branched C₁₋₁₀ carboxylic acid, straight orbranched C₁₋₁₀ acetal, straight or branched C₁₋₁₀ alkyl including atleast one hydroxyl group, straight or branched C₁₋₁₀ ester including atleast one hydroxyl group, straight or branched C₁₋₁₀ ketone including atleast one hydroxyl group, straight or branched C₁₋₁₀ carboxylic acidincluding at least one hydroxyl group, and straight or branched C₁₋₁₀acetal including at least one hydroxyl group; and R₃, R₄, R₅, R₆ and R₇independently represent hydrogen or methyl; and a, b and c individuallyrepresent the relative amount of each comonomer. Preferably, the ratio a: b: c=10-89 mol %: 10-89 mol %: 1-40 mol %.

EXAMPLE 3

(i) As a 1^(st) comonomer, 0.09 mole of the compound of Chemical Formula4 obtained from Example 1, (ii) as a 2^(nd) comonomer, 0.1 mole ofmaleic anhydride represented by following Chemical Formula 8 and (iii)as a 3^(rd) comonomer, 0.01 mole of acrylic acid represented byfollowing Chemical Formula 9 were put into a 200 ml of round bottomflask. After adding thereto 0.2 g of AIBN, as a polymerizationinitiator, and 8 g of tetrahydrofuran, as a solvent, the reactants werereacted under a nitrogen or argon atmosphere at 65° C. for 10 hours.After completion of the polymerizing reaction, the resultant solutionwas precipitated in ethyl ether solvent and the precipitant was vacuumdried to obtain a photoresist cross-linker copolymer of followingChemical Formula 10.

<Chemical Formula 8>

<Chemical Formula 9>

<Chemical Formula 10>

EXAMPLE 4

The procedure of Example 3 was repeated, but using the cross-linkermonomer of Chemical Formula 5 obtained from Example 2 instead of thecross-linker monomer of Chemical Formula 4 obtained from Example 1, toobtain a cross-linker copolymer represented by the following ChemicalFormula 11.

<Chemical Formula 11>

EXAMPLE 5

The procedure of Example 3 was repeated but using5-norbornene-2-carboxylic acid (represented by the following ChemicalFormula 12) instead of acrylic acid of Chemical Formula 9, to obtain across-linker copolymer represented by the following Chemical Formula 13.

<Chemical Formula 12>

<Chemical Formula 13>

EXAMPLE 6

The procedure of Example 3 was repeated but using (i) as a firstcomonomer, the cross-linker monomer of Chemical Formula 5 instead ofChemical Formula 4 and, (ii) as a third comonomer,5-norbornene-2-carboxylic acid represented by Chemical Formula 12instead of acrylic acid of Chemical Formula 9, to obtain a cross-linkercopolymer represented by the following Chemical Formula 14.

<Chemical Formula 14>

EXAMPLE 7

The procedure of Example 3 was repeated but using the compoundrepresented by the following Chemical Formula 15 instead of acrylic acidof Chemical Formula 9 as a third comonomer, to obtain a cross-linkercopolymer represented by the following Chemical Formula 16.

<Chemical Formula 15>

<Chemical Formula 16>

EXAMPLE 8

The procedure of Example 3 was repeated but using (i) as a firstcomonomer, the cross-linker monomer of Chemical Formula 5 instead ofChemical Formula 4 and, (ii) as a third comonomer, the compoundrepresented by the above-mentioned Chemical Formula 15 instead ofacrylic acid of Chemical Formula 9, to obtain a cross-linker copolymerrepresented by the following Chemical Formula 17.

<Chemical Formula 17>

EXAMPLE 9

The procedure of Example 3 was repeated but using the compoundrepresented by the following Chemical Formula 18 instead of acrylic acidof Chemical Formula 9 as a third comonomer, to obtain a cross-linkercopolymer represented by the following Chemical Formula 19.

<Chemical Formula 18>

<Chemical Formula 19>

EXAMPLE 10

The procedure of Example 3 was repeated but using the compoundrepresented by the following Chemical Formula 20 instead of acrylic acidof Chemical Formula 9 as a third comonomer, to obtain a cross-linkercopolymer represented by the following, Chemical Formula 21.

<Chemical Formula 20>

<Chemical Formula 21>

Preparation Of Photoresist Composition And Pattern Forming Process

The preparation process for a negative photoresist composition using thecross-linkers of the present invention will be described below:

Since the cross-linkers of the present invention are of the chemicalamplification type, a photoresist composition of the present inventioncontains (i) a photoresist resin, (ii) a cross-linker according to thepresent invention (iii) a photoacid generator and (iv) an organicsolvent for mixing them.

The above-mentioned photoresist resin may be a conventional photoresistpolymer, preferably one that is suitable for use in a photolithographyprocess employing extremely short-wavelength light (below 250 nm).

As the photoacid generator, conventional photoacid generators such asonium-type compounds, halogen-containing compounds, diazoketonecompounds, sulfone, sulfonic acid and sulfonium compounds may be used,most preferably, sulfonium compounds. For example, the photoacidgenerator may be diphenyl iodide hexafluorophosphate, diphenyl iodidehexafluoroarsenate, diphenyliodide hexafluoroantimonate, diphenylp-methoxyphenyl triflate, diphenyl p-toluenyl triflate, diphenylp-isobutylphenyl triflate, diphenyl p-tert-butylphenyl triflate,triphenylsulfonium hexafluorophosphate, triphenylsulfoniumhexafluoroarsenate, triphenylsulfonium hexafluoroantimonate,triphenylsulfonium triflate, dibutylnaphthylsulfonium triflate or amixture thereof.

As an organic solvent, 2-methoxyethylacetate, ethyl 3-ethoxypriopionate,methyl 3-methoxypropionate, cyclohexanone, propylene glycol methyl etheracetate, or the like may be used.

In order to form a photoresist pattern using the photoresist compositionthus prepared, the photoresist composition is spin-coated on a siliconwafer, and “soft-baked” in an oven or on hot-plate, at a temperature ofabout 70° C. to 200° C., preferably 80° C. to 150° C., for about 1 to 5minutes. Then, the photoresist layer is exposed to 0.1 to 100 mJ/cm² oflight energy using an exposer with ArF, KrF, E-beam, EUV or X-rayradiation, and “post-baked” at a temperature of about 70° C. to 200° C.,preferably 100° C. to 200° C. Then, the wafer is developed by dippingthe exposed wafer into an alkaline developing solution such as 0.01-5 wt% of TMAH (tetramethylammonium hydroxide) solution, preferably 2.38 wt %or 2.5 wt % TMAH solution, for a predetermined time, preferably about 40seconds, to obtain a ultramicro photoresist pattern.

EXAMPLE 11

First, a photoresist composition was obtained by dissolving (i) 1 g ofthe photoresist resin having the following Chemical Formula 22 (ii) 10 gof the photoresist cross-linker of Chemical Formula 4 obtained fromExample 1 and, (iii) 0.6 g of triphenylsulfonium triflate as a photoacidgenerator in (iv) 66 g of 2-methoxyethyl acetate solvent.

Chemical Formula 22>

wherein d, e and f individually represent the relative amounts of eachcomonomer.

The photoresist composition thus prepared was spin-coated on a siliconwafer, and soft-baked at 110° for 90 seconds. After baking, the waferwas exposed using an ArF exposer, and then developed by being dipped in2.38 wt % aqueous TMAH (tetramethylammonium hydroxide) solution for 40seconds. Thereafter, the wafer was post-baked at 110° C. for 90 secondsto obtain a 0.13 μm L/S pattern (FIG. 1).

The results show that the hardening of the exposed region was excellenteven though the exposure energy was merely 15 mJ/cm², due to the goodcross-linking property of the cross-linker used.

EXAMPLE 12

The procedure of Example 11 was repeated but using the same amount ofthe cross-linker of Chemical Formula 5 instead of Chemical Formula 4, toobtain a negative pattern with a resolution of 0.20 μm L/S (FIG. 2).

EXAMPLE 13

The procedure of Example 11 was repeated but using (i) the compound ofthe following Chemical Formula 23 instead of Chemical Formula 22 as thephotoresist polymer, and (ii) a compound of Chemical Formula 10 insteadof Chemical Formula 4 as the cross-linker, to obtain a negative patternwith a resolution of 0.20 μm L/S (FIG. 3).

<Chemical Formula 23>

wherein d, e and f individually represent the relative amounts of eachcomonomer.

EXAMPLE 14

The procedure of Example 11 was repeated but using (i) the compound ofthe following Chemical Formula 24 instead of Chemical Formula 22 as thephotoresist resin, and (ii) a compound of Chemical Formula 11 instead ofChemical Formula 4 as the cross-linker, to obtain a negative patternwith a resolution of 0.20 μm L/S (FIG. 4).

<Chemical Formula 24>

wherein d, e and f individually represent the relative amounts of eachcomonomer.

EXAMPLE 15

The procedure of Example 11 was repeated but using (i) the compound ofthe following Chemical Formula 25 instead of Chemical Formula 22 as thephotoresist resin, and (ii) a compound of Chemical Formula 13 instead ofChemical Formula 4 as the cross-linker, to obtain a negative patternwith a resolution of 0.20 μm L/S (FIG. 5).

<Chemical Formula 25>

wherein d, e and f individually represent the relative amounts of eachcomonomer.

EXAMPLE 16

The procedure of Example 11 was repeated but using (i) the compound ofthe following Chemical Formula 26 instead of Chemical Formula 22 as thephotoresist resin, and (ii) a compound of Chemical Formula 14 instead ofChemical Formula 4 as the cross-linker, to obtain a negative patternwith a resolution of 0.20 μm L/S (FIG. 6).

<Chemical Formula 26>

wherein d, c and f individually represent the relative amounts of eachcomonomer.

EXAMPLE 17

The procedure of Example 11 was repeated but using (i) the compound ofChemical Formula 24 instead of Chemical Formula 22 as the photoresistresin, and (ii) a compound of Chemical Formula 16 instead of ChemicalFormula 4 as the cross-linker, to obtain a negative pattern with aresolution of 0.20 μm L/S (FIG. 7).

EXAMPLE 18

The procedure of Example 11 was repeated but using (i) the compound ofChemical Formula 24 instead of Chemical Formula 22 as the photoresistresin, and (ii) a compound of Chemical Formula 17 instead of ChemicalFormula 4 as the cross-linker, to obtain a negative pattern with aresolution of 0.20 μm L/S (FIG. 8).

EXAMPLE 19

The procedure of Example 11 was repeated but using (i) the compound ofChemical Formula 24 instead of Chemical Formula 22 as the photoresistresin, and (ii) a compound of Chemical Formula 19 instead of ChemicalFormula 4 as the cross-linker, to obtain a negative pattern with aresolution of 0.20 μm L/S (FIG. 9).

EXAMPLE 20

The procedure of Example 11 was repeated but using (i) the compound ofChemical Formula 24 instead of Chemical Formula 22 as the photoresistresin, and (ii) a compound of Chemical Formula 21 instead of ChemicalFormula 4 as the cross-linker, to obtain a negative pattern with aresolution of 0.20 μm L/S (FIG. 10).

As described above, the photoresist cross-linker according to thepresent invention has high cross-linking ability. Thus, a photoresistcontaining the cross-linker exhibits an outstanding difference in curingbetween exposed regions and non-exposed regions which makes it possibleto form a fine pattern with good profile. In addition, since thephotoresist cross-linker is of the chemical amplification type, it ispossible to obtain the desired effect using a small amount of photoacidgenerator, which solves the problems caused by a large amount ofphotoacid generator being contained in the photoresist composition.Furthermore, since the photoresist cross-linker according to the presentinvention has high light-sensitivity, it is possible to obtain asufficient exposure effect with a small quantity of light radiation.Accordingly, a photoresist composition containing the cross-linker ofthe present invention is suitable for use in a photolithography processemploying extremely short wavelength light, such as ArF (193 nm).

What is claimed is:
 1. A photoresist cross-linker wherein saidcross-linker is a copolymer comprising (i) a photoresist cross-linkermonomer of chemical formula 1, as a 1^(st) comonomer: <Chemical Formula1>

wherein X₁ and X₂ individually represent CH₂, CH₂CH₂, O or S; p is aninteger from 0 to 5; R₁ and R₂ independently represent straight orbranched C₁₋₁₀ alkyl, straight or branched C₁₋₁₀ ester, straight orbranched C₁₋₁₀ ketone, straight or branched C₁₋₁₀ carboxylic acid,straight or branched C₁₋₁₀ acetal, straight or branched C₁₋₁₀ alkylincluding at least one hydroxyl group, straight or branched C₁₋₁₀ esterincluding at least one hydroxyl group, straight or branched C₁₋₁₀ ketoneincluding at least one hydroxyl group, straight or branched C₁₋₁₀carboxylic acid including at least one hydroxyl group, and straight orbranched C₁₋₁₀ acetal including at least one hydroxyl group; and R₃ andR₄ independently represent hydrogen or methyl, and (ii) maleic anhydrideas a 2^(nd) comonomer.
 2. A photoresist cross-linker according to claim1 wherein said copolymer further comprises (iii) acrylic acid ormethacrylic acid, as a 3^(rd) comonomer, and is represented by followingChemical Formula
 6. <Chemical Formula 6>

wherein X₁ and X₂ individually represent CH₂, CH₂CH₂, O or S; p is aninteger of 0 to 5; R₁ and R₂ independently represent straight orbranched C₁₋₁₀ alkyl, straight or branched C₁₋₁₀ ester, straight orbranched C₁₋₁₀ ketone, straight or branched C₁₋₁₀ carboxylic acid,straight or branched C₁₋₁₀ acetal, straight or branched C₁₋₁₀ alkylincluding at least one hydroxyl group, straight or branched C₁₋₁₀ esterincluding at least one hydroxyl group, straight or branched C₁₋₁₀ ketoneincluding at least one hydroxyl group, straight or branched C₁₋₁₀carboxylic acid including at least one hydroxyl group, and straight orbranched C₁₋₁₀ acetal including at least one hydroxyl group; and R₃, R₄and R₅ independently represent hydrogen or methyl; and a, b and cindividually represent the relative amounts of each comonomer.
 3. Aphotoresist cross-linker according to claim 1 wherein said copolymerfurther comprises (iii) a compound represented by following Chemicalformula 27, as a 3^(rd) comonomer: <chemical formula 27>

said copolymer being represented by the following Chemical Formula 7:<Chemical Formula 7>

wherein X₁ and X₂ individually represent CH₂, CH₂CH₂, O or S; Z₁ and Z₂individually represent CH₂, CH₂CH₂, O or S; p and q individuallyrepresent an integer of 0 to 5; R₁, R₂, R₈, R₉, R₁₀ and R₁₁independently represent straight or branched C₁₋₁₀ alkyl, straight orbranched C₁₋₁₀ ester, straight or branched C₁₋₁₀ ketone, straight orbranched C₁₋₁₀ carboxylic acid, straight or branched C₁₋₁₀ acetal,straight or branched C₁₋₁₀ alkyl including at least one hydroxyl group,straight or branched C₁₋₁₀ ester including at least one hydroxyl group,straight or branched C₁₋₁₀ ketone including at least one hydroxyl group,straight or branched C₁₋₁₀ carboxylic acid including at least onehydroxyl group, and straight or branched C₁₋₁₀ acetal including at leastone hydroxyl group; and R₃, R₄, R₆ and R₇ independently representhydrogen or methyl; and a, b and c individually represent the relativeamounts of each comonomer.
 4. A photoresist cross-linker according toclaim 1, wherein the photoresist cross-linker is selected from the groupconsisting of the compounds represented by following Chemical Formulas10, 11, 13, 14, 16, 17, 19 and
 21. <Chemical Formula 10>

<Chemical Formula 11>

<Chemical Formula 13>

<Chemical Formula 14>

<Chemical Formula 16>

<Chemical Formula 17>

<Chemical Formula 19>

<Chemical Formula 21>

wherein a, b and c independently represent the relative amounts of eachcomonomer.
 5. A photoresist cross-linker according to one of claims 2 to4, wherein the ratio of a: b: c is 10-89 mol %: 10-89 mol %: 1-40 mol %.6. A photoresist composition comprising (i) a photoresist resin, (ii) aphotoresist cross-linker according to claim 1, (iii) a photoacidgenerator, and (iv) an organic solvent.
 7. A photoresist compositionaccording to claim 6, wherein the photoresist resin comprises aconventional photoresist polymer containing more than one hydroxylgroup.
 8. A photoresist composition according to claim 7, wherein thephotoresist resin is selected from the group consisting of the compoundsrepresented by following Chemical Formulas 22 to
 26. <Chemical Formula22>

<Chemical Formula 23>

<Chemical Formula 24>

<Chemical Formula 25>

<Chemical Formula 26>

wherein d, e and f independently represent the relative amounts of eachcomonomer.
 9. A photoresist composition according to claim 6, whereinthe photoacid generator is selected from the group consisting ofdiphenyl iodide hexafluorophosphate, diphenyl iodide hexafluoroarsenate,diphenyliodide hexafluoroantimonate, diphenyl p-methoxyphenyl triflate,diphenyl p-toluenyl triflate, diphenyl p-isobutylphenyl triflate,diphenyl p-tert-butylphenyl triflate, triphenylsulfoniumhexafluorophosphate, triphenylsulfonium hexafluoroarsenate,triphenylsulfonium hexafluoroantimonate, triphenylsulfonium triflate,dibutylnaphthylsulfonium triflate and mixtures thereof.
 10. Aphotoresist composition according to claim 6, wherein the organicsolvent is selected from the group consisting of 2-methoxyethylacetate,ethyl 3-ethoxypriopionate, methyl 3-methoxypropionate, cyclohexanone,propylene glycol methyl ether acetate and mixtures thereof.